Stage lighting fixtures are known comprising a casing with a closed first end and open second end; a light source housed inside the casing, close to the closed first end, and which emits a light beam along an optical axis; and an optical assembly positioned to intercept the light beam.
Lighting fixtures of this type are unable to produce a perfect, strong beam, i.e. produce a strong beam, but with chromatic defects in the form of a halo of a different colour from the beam.